In general, an air conditioner refers to an apparatus for cooling or heating an interior space. The air conditioner includes a compressor for compressing refrigerant, a condenser for condensing refrigerant discharged from the compressor, an expander for expanding refrigerant passing through the condenser and an evaporator for evaporating refrigerant expanded by the expander.
A turbo refrigerator may include a compressor for compressing low-pressure refrigerant into high-pressure refrigerant, a condenser, an expansion valve and an evaporator to perform a refrigeration cycle.
The turbo refrigerator includes a centrifugal type turbo compressor (hereinafter, turbo compressor). The turbo compressor discharges gas in a high-pressure state while converting kinetic energy generated by a driving motor into static energy and may include one or more impellers rotating by driving force of the driving motor to compress refrigerant and a housing in which the impellers are mounted.
In addition, the turbo compressor may include a bearing supporting axial force applied to a rotation shaft in a process of rotating the impeller connected to the rotation shaft at high speed.
In general, representative examples of the bearing used for the turbo compressor include a magnetic bearing. More specifically, when a voltage is applied to the magnetic bearing in order to support axial force applied to the rotation shaft, magnetic force is generated. Using the generated magnetic force, the magnetic bearing supports the rotation shaft in a non-contact manner, thereby reducing loss due to friction generated by contact with the rotation shaft and rotating the rotation shaft at a high speed.
In addition, when the magnetic bearing is used in the turbo compressor, a backup bearing may be formed in order to efficiently support the rotation shaft even when the voltage is not applied to the magnetic bearing or an error occurs in the magnetic bearing.
That is, one side of the rotation shaft may support the magnetic bearing and the other side thereof may support the backup bearing, thereby always stably supporting the rotation shaft.
The center of the magnetic bearing may be defined as a “magnetic center” and the center of the backup bearing may be defined as a “mechanical center”. If the magnetic center and the mechanical center are aligned, when the voltage is applied to the magnetic bearing, the rotation shaft is stably supported and rotated.
However, when the magnetic center and the mechanical center are not aligned, the rotation shaft does not appropriately rotate, thereby mechanically damaging the turbo compressor. When the magnetic center and the mechanical center are not aligned, an error between the centers may be defined as a “center error”.
From the viewpoint of management of quality of the turbo compressor, it is necessary to measure the “center error” in order to align the magnetic center and the mechanical center.
However, in the related art, a levitation controller was used to measure the center error. The levitation controller uses a method of assembling the magnetic bearing and the backup bearing in the rotation shaft and rotating the rotation shaft in a state of inserting the assembled device into the levitation controller to measure the center error between the magnetic bearing and the backup bearing.
However, the conventional center error measurement method has the following problems.
First, the levitation controller for measuring the center error is required. In particular, the center error cannot be measured without the levitation controller.
Second, in the levitation controller, measurement can be performed in a state in which the magnetic bearing and the backup bearing are both assembled in the rotation shaft. That is, since the center error can be measured in a state of assembling the magnetic bearing, the rotation shaft and the backup bearing, failure of a product can be checked but a product cannot be disassembled and reassembled. That is, the center error can be measured after assembly.